[NaterGator]

I suspect there are some obfuscated dampening and oscillatory properties of this circuit which make them unpredictable.

Thevenin equivalents are not all that bad... it's no different than general relativity and the idea that gravity and accelerated motion are indistinguishable. I will admit though that Thevenin equivs are not quite so straight forward until you do some "hands on" with them.

I think the biggest problem with modeling may be if the needle is resisted by a spring. I suspect the spring will probably act progressive and I doubt I'll have equipment sensitive enough to accurately describe the spring's effect on the needle.


Our whacko city Government can't surprise me anymore. They just approved 8 story commercial buildings on the corner of Univ. and 13th where they have already sold 200% more living space than they have provided parking spots, and now in the same area 2 more apt buildings are finishing with zero parking provisions and then University Corners will go up... it's just plain stupid, but it's G-Ville.

[RavenTai]

Originally Posted by NaterGator

Thevenin equivalents are not all that bad... it's no different than general relativity and the idea that gravity and accelerated motion are indistinguishable. I will admit though that Thevenin equivs are not quite so straight forward until you do some "hands on" with them.

If you say so, I found the formula online and dropped in the numbers I thought in the right spot but all I got out was garbage, I did not know enough about it to figre out what I was doing wrong, for me in the end it was just easier to get it close on paper and then tweak it via trial and error. I had a spare gauge and a heat source, digital thermometer & power supply all set up in a test bed.

[Darwood]

Originally Posted by NaterGator

Maybe it will be worthwhile for me to try and more accurately model the circuit -> needle position correlation... eventually I would love to script up something where different circuits can be "built" and a virtual gauge can be toyed with. I'm fairly confident I have the necessary math/calculus background to accurately describe all said circuits and the needle position, I suppose it would come down to the necessity of a predictable and fairly accurate needle solution from Toyota (read: no varying resistive-spring tensioning on the needle) as well as decent measurements of the components to describe everything mathematically.

This would be great. The problems I was finding was that the resistor and temperature values for the temp sensor when measured alone didn't quite match up with the temperatures and resistor values that were determined by Raven's test. I used the test values instead and was able to get a mostly consistent model. Unfortunately my notes are like my methods, jumbled thoughts and in storage (literally in storage).

It sounds to me like to 100+150 combo is a little too numb for a hot climate like Florida and the 50+110 combo is a little to sensitive. Hrm hrm hrm... decisions decisions.

Where do you want the extremes? I did run some other resistors for a while that might give you more what you want. I posted some of the results in the development thread.

http://forum.ih8mud.com/80-series-tech/53142-adding-coolant-temp-gauge-10.html

[NaterGator]

Well I did the mod today with what I had on hand while my oil drained which was the 50+110 combo and it is working so far from my limited trials. It looks like the needle rests pretty standardly horizontal and does climb slightly with low speed (ie low airflow) usage, but it has been cooler here as well.

I'll let it rest until I have a reason to muck with it, and if I do I'll probably do so over the summer and dig deeper into the construction.

[KliersLC]

RT, great job on the R&D for this. I did it last week and didn't have too many problems. Couple of notes though, the 93-94 dash comes apart a little different as you have noted; the piece that wraps over the steering column is the same piece that holds all the temp controls and various buttons, so you have to unplug all of those as well.

It is a great time to put in the CDL switch though, and also rearrange any of the buttons that you would like in different places. The key to getting that piece off is removing the screw by the hand throttle and then all five of the screws behind the ash tray.(this may not be "needed" but it makes it easier to move that big expensive piece of plastic around. Two screws pointing outboard diagonally on either side, one pointing up diagonally at the center, and two pointing straight up just under the lip. It also isn't neccesary to remove the steering column cover, I had most everything back together when I noticed that the odometer knob wasn't sticking out through the hole, so I had to pull it back apart.

Also, the 93-94 board doesn't seem to require drilling out the holes where the diode was.

X2 on the solder braid sucking, and one last thing:

I tried to be cool and bend the resistor over like your post shows, but I put mine on the inside, and when I pushed on it, the metal strip separated from the board, and I had to superglue it back on. So, be careful with the circuit board, and don't bother making it look pretty, not too many people will look in there.


Thanks again!

Dan

[semlin]

dan, let me know where your needle sits. mine sits somewhere above the half way point after hill climbs or on sustained highway driving. i'd like to know if it is a 93-94 trait.

[KliersLC]

Mine seems to sit just below half for the most part, but climbs to just above half only on hills. I haven't run it in hot weather yet, or with AC in town, so time will tell. My stock fan clutch works really well and the coolant is fresh, so that may be part of it. I drove it about 300 miles last week, bur after reading this thread, I have come to ignore the thing, so I didn't take notice of what it was doing very often. I'll pay attention more this week and post back with results.

[RavenTai]

Thanks for posting up dash tips for the 93/94 trucks, I figured it would be different but did not have one around to add any notes.

Originally Posted by KliersLC

I tried to be cool and bend the resistor over like your post shows, but I put mine on the inside, and when I pushed on it, the metal strip separated from the board, and I had to superglue it back on. So, be careful with the circuit board, and don't bother making it look pretty, not too many people will look in there.


Thanks again!

Dan

you were suppose to bend the resistor legs before you put it in

[KliersLC]

Originally Posted by RavenTai

Thanks for posting up dash tips for the 93/94 trucks, I figured it would be different but did not have one around to add any notes.





you were suppose to bend the resistor legs before you put it in

Oh. I must have missed that part.

[RavenTai]

got asked this via PM figured some others might the same question so posting it here

Originally Posted by m

Raven,

Thanks for the reply. It helps! My main purpose is to find out if I need any special or extra cooling for the HOT resistor. I know the answer now since it is not going to be as hot as the old one.

No problem, go ahead to include my question in the thread. Please let me know if you want me to post the question so that you can reply.

Thanks again.

[KliersLC]

Semlin, I put 700 miles on the 80 last weekend, and sustained freeway driving puts the needle just below half, and long 4th gear hills bring it up to right at horizontal, but it never gets higher than that. We'll see how she does when it warms up a bit.

Thanks again RT!
Dan

[semlin]

thanks dan. so on long hills it moves up a needle width?

i did a 500 mile round trip on the weekend and even with a torqued up fan clutch and cool conditions I run consistently just above the line and spike up on hills two or three needle widths.

time for a new rad.

[NaterGator]

Semlin, I have the same experience. In hot weather with the AC, under prolonged load I will see a 2-3 needle width jump in temps. In reality though my OBDII scanner says my coolant temp only goes up to 197°F from 190°F when it shows that much deflection, so I hardly think it's something to worry about, especially since I never see it go past ~ that mark.

[semlin]

i get that in cold weather without a load and without AC. in hot weather i get that much defelection just by turning the ac on. in just barely warm weather with no ac i go up a long hill and I still get up to 206ish not dangerous but not right. the normal op temp according to my FSM is up to 203.

[KliersLC]

Are you running green or red; and what mix?

I don't remember how much a new radiator is, but if you haven't already, I'd check everything else first.

[semlin]

red. I have been putting this off too long. everything else has been done, including a seriously amped up fan clutch. i just checked my plugs on the weekend and they are 100% normal. there is no sign I am running lean. my gauge was RT's beta for the 93-94s so I have his precise temp measurement photos.

[JO MAOMA]

i took RT's advice and order extra resistors while i was at it
(shipping was the same). i've got 4 sets left that i'll toss in
the mail to anyone that wants to do the mod...

[JO MAOMA]

three sets left...




...did i mention they're free!

edit: all gone, thanks!

[RavenTai]

Originally Posted by JO MAOMA

i took RT's advice and order extra resistors while i was at it
(shipping was the same). i've got 4 sets left that i'll toss in
the mail to anyone that wants to do the mod...

Originally Posted by JO MAOMA

three sets left...




...did i mention they're free!

edit: all gone, thanks!

[94landcruiser]

Just did my second one (using the resistors I bought as backup last year) I was happy the way it was but now that I have read the ensuing posts I wish I had looked here before I did it so I could have bought Darwood's resistors.

Thanks to everyone for the great info you provide!


I LOVE MUD!

[94landcruiser]

I just got back from my first drive. I was a bit taken aback, The gauge sits at 3/4 (much higher than the 94's gauge did with the same 100/50 resistors) and sitting in 95 degree temp @ in & out just now (cool for Phoenix lately) it climbed to 1.5-2 needles widths from the bottom of the red. There is no indication from the engine that is is getting hot and all is well there.

Are later year gauges different? I think this cluster is from a late year or maybe a Lexus because the speedo and tach needles are luminescent as opposed to my old ones from the 94 which were painted.


I'd appreciate any input on this please.

Thanks.

[medtro]

Which one did you follow?

http://forum.ih8mud.com/showpost.php...&postcount=151

http://forum.ih8mud.com/showpost.php...&postcount=158

I believe the 2nd link is the correct one.

[94landcruiser]

I honestly don't know which thread it came from. I saved it to a word doc 5/16/06 it used 110/50 ohm resistors which I bought two sets of last year, here is that doc:

Remove the gauge from the cluster. first the cluster splits in two, the gauges and a white backing are one half, the "glass" and black mask in the other. There are clips around the perimeter lift each one in turn by hand and the two halves will split, after the glass is off be careful not to set the cluster on its face, the cards and needles are kind of fragile. Try not to not touch the face cards of any of the gauges, fingerprints leave marks, there are 4 screws (see pic) back these screws out partially and then press them with moderate finger pressure. the gauge will seam stuck at first but then will pop up a little bit, if is fells wrong or partially attached stop and give it a good looking over, completely remove the screws and then work the gauge out, it had some slight interference with the tack card but it can be worked out of there. Be careful the tach needle does not receive any load.



Modify the gauge

If you do not know how to work with solder give these a read

http://www.circuittechctr.com/guides/7-1-1.shtml

http://www.epemag.wimborne.co.uk/solderfaq.htm

First need to secure the gauge so that you will have two free hands but the gauge is not resting on the needles, there is an area of the PCB that can be clamped in a vice at a corner, when you need to apply even light force to the PCB also support it with your hand, do not bend the PCB.

More secure clamping method provided by Rookie2 http://forum.ih8mud.com/showpost.php...4&postcount=58


The two components we are interested in are a 75 ohm resistor and a Zener diode (see pic) both of these have two connections each for a total of 4 connections, the resistor looks somewhat like a peanut and is just over ¼” long on the back of the PCB it is marked with a zig-zag line , the zener diode is a tiny red bead it is marked on the PCB by a rectangle with a stripe at one end.

First we need to remove both of these components, de-solder these 4 connections straighten out the wires and push them through, if you have any troubles with them hanging up on solidified solder use the tip of your soldering iron. Using the soldering iron as a tool is handy as it will keep the solder flowing wile you move stuff around. Then remove any excess solder as necessary to have the holes open to allow insertion of the new components, a small amount of solder left on the pad of the PCB is acceptable and actually desirable.

The 110 Ohm resistor will replace the 75 ohm resistor; first bend the leads of the resistor to until they are parallel to each other and perpendicular to the resistor. You do not want to bend them tight right as it comes out of the resistor, this may form cracks in the wire that could cause the lead to break with vibration rendering the gauge useless. Set a ~1/8” drill bit against the resistor touching both the resistor and the lead, bend the lead 90* over the bit this will form a radius. You want the two legs spaced as close as possible to the width of the two holes in the PCB, trim the two leads just enough to get between the PCB and the face card of the gauge, This resistor can get hot in use so we want air flow around it, we also want to keep it away from the clear plastic light guide and the needle motor, I let it naturally hang with gravity and put it closer to the PCB (but not to close) than the face card and it seamed about right (see pic) solder it in place then trim the excess lead.

The zener diode is replaced with the 50 ohm resistor. The holes for the zener diode were smaller than the leads of the resistor, chuck up a very small drill bit (same size as the lead of the resistor) in a drill and turn the chuck by hand to enlarge the holes. These holes are closer together than the width of the resistor so you will need to bend one of the legs into a joggle, make a180° bend at the end of the resistor then a 90°bend at about the middle of the resistor, bend the other one 90* at a location that will achieve proper spacing, trim the leads so that more than enough will go through the hole to support the resistor. this resistor does not get hot and due to its location is easier to install this one on the bottom of the PCB opposite of the other resistor. There is clearance in the cluster to do so just keep it tight against the PCB (see pic)


If you have a meter check the connections. the resistance of the joints should no be more than 1 ohm higher than the resistance you get with your probes touched together, Check the resistance from the sense post (top post in the pictures) to the two close legs of the two resistors, the other leg of the 110 ohm resistor is checked to the + post (lower left in the pictures) , the other leg of the 50 ohm resistor is checked to the nut marked “U”, there is a thin coating on the nut you need to pierce to make a connection


Results

You now have a gauge that will move with all temperature changes within its sensitive range.


Full sweep peg to peg is 94°

Pegged hot 244°
Top of red is 227°
Bottom of red 217°
Center is approximately 189°
Cold line is 160°
Pegged cold 150°



Notes



“Center” is pretty much horizontal. It is the middle between the bottom of red and the cold line, witch is not the same as center of the full range of the gauge. Some describe “center” as the just below the middle, also the needle sits high above the face card with the markings making it quite susceptible to parallax error, at any rate after warm up wherever your needle sat before mod is the “center” point for our purposes.

Please give feedback on how this goes for you. And what changes can be made in the directions to make it clearer. If you find any tips or tricks along the way please post 'um up

93-94 trucks Thanks to the effort of Semlin a mod is in the works.

Edit 3-15-05, the same mod also works for 93-94 trucks within a few degrees, accessing the gauge may be a little diffrent as the dash is diffrent on the 93-94 trucks, if anybody does one of these would you mind taking notes on accessing the guage.

[KliersLC]

I'll let RT chime in on the specifics, but you might double check to make sure your fan clutch is working right. Another good check would be to hook it up to a scanner to see what the actual water temp is, and then check that against your modded gauge. You wouldn't be the first to find that your truck was running hotter than you thought......

BTW, I think RT has an LX

[94landcruiser]

Thanks for the input, literally the entire cooling system is new, replaced with the HG in May, less than 3k ago.

With the gauge from the original cluster and the 110/50 resistors it ran like it was painted in the middle. Before the mod it was like it was painted @ the 1/4 point. I don't care where it runs as long as it is reliable.

I am going to the mechanic next week to get the ARB I ordered I'll ask him to check the temp with his computer then.

Thanks

[94landcruiser]

I just came back from a intensive drive/temp measuring trip. I bought a laser thermometer and took readings/pictures of the gauge.

The temp was never above 202 (at the waterpump/head/hoses etc)

If there is somewhere else I need to point the laser at please let me know.


This is after several red lights:


This is in the parking lot after I got the laser, the temps were waterpump 199, radiator 202, overflow tank (open cap) 165, head 202, block 212.



The angle makes it look closer to the red than it is it is about 1.5 needle widths away ( closer than I am comfortable with) but if the actual temps mean the cooling system is ok I guess I'll get used to it.

This is on the freeway about a minute after it cooled from from the first picture.

The odd thing is with the other gauge it never got above 3/4 . btw ambient was 106 during this time.

[Rookie2]

Originally Posted by 94landcruiser

btw ambient was 106 during this time.

At that ambient temp, I'm not suprised you'd get spikes near the red. On trips with temps in the mid 90's, AC on and stopping for gas, I've had spikes near that. Definitely increases the pucker fact a little.


Rookie2

[Darwood]

Originally Posted by 94landcruiser

This is in the parking lot after I got the laser, the temps were waterpump 199, radiator 202, overflow tank (open cap) 165, head 202, block 212.

If the coolant at the sensor was 212 like the block temperature, the above photo is about what 212 should look like with the 110/50 ohm resistors. Actually it's more what 214 should look like but the angle might be making it seem higher. The real question is if that is in fact the coolant temperature.

[RavenTai]

94LC, Bottom of red on my 96 came out to 217, on Semlins 93 gauge it came out to 213, I dont know if the difference is random gauge to gauge variation or a 93-96 difference but they are close either way


Your 1.5 to 2 needle width from red at 212 sounds like you red line is 217 or so,

For reference the AC will cut out at 226 and come back on as temps decrease at 217, 212 is hot but not quite time to pull over,

thermostat openign temp is 179.6 (82C) so 212 is 32.4F over that,


the 202 water pump temp is thought provoking, the coolant coming out the the bottom of the radiator should be cooler than that even with a 106 ambient, your cooling system is working with a 10F delta between inlet and outlet, not much,

I would look at the blue hub fan clutch mod,

How is your radiator?

[94landcruiser]

Thanks. Everything radiator, waterpump, hoses, thermostat, etc were replaced in May.I don't know if he also did the fan clutch. the truck had 166,xxx and has 168,xxx now. I am taking it to the shop tomorrow and will have him have a look.

I used the 110 & 50 resistors btw. It is 90 mow as soon as the Yankee game ends I will go for a ride and report.